The present invention relates to a method for restoring silicone-polycarbonate parts which have been rejected during the manufacture of such articles. More particularly, the present invention relates to the use of an aqueous alkaline bath to treat a silicone-polycarbonate part comprising a silicone hardcoat layer, an intermediate thermoplastic acrylic primer layer and a polycarbonate substrate to effect the selective removal of a defective silicone hardcoat layer.
During the manufacture of polycarbonate parts having a silicone hardcoat and an intermediate thermoplastic acrylic primer layer, several parts are often rejected due to a defective silicone hardcoat. A typical coating procedure used to make silicone hardcoat polycarbonate articles is shown by Goossens et al., U.S. Pat. No. 4,242,381, Olson et al., U.S. Pat. No. 4,284,685 and Patel, U.S. Pat. No. 5,041,313 which are incorporated herein by reference.
A procedure for salvaging organic thermoplastic values from discarded thermoplastic articles having a decorative or protective coating is shown in copending application of Gillette et al., Ser. No. 07/981,668, filed Sep. 25, 1992. Among the articles which can be treated are silicone-polycarbonate composites which can be in granulated form. During the treatment of the composites, the silicone hardcoat is removed; if these composites have an acrylic primer, it also is removed. The resulting thermoplastic polycarbonate can then be reextruded and remolded. The remolded polycarbonate then has to be reprimed and hardcoated.
It would be desirable therefore to provide a satisfactory procedure for salvaging defective silicone-polycarbonate composites, such as intact headlamp-lenses having both a thermoplastic acrylic primer and a silicone hardcoat. It also would be desirable to avoid the requirement of having to remold such rejected parts, or the need to reprime such polycarbonate substrates after the silicone hardcoat has been removed.